Statistical Characteristics of Precipitation in Summer in Beijing Area during 2007-2011

Using hourly precipitation data from 237 automatic weather stations in Beijing area from June to August 2007-2011, the fine-scale spatiotemporal distribution of precipitation and the effect of the city on local precipitation in Beijing were studied. Based on the analysis, the major findings can be summarized as follows: Firstly, in most areas of Beijing, the average number of effective precipitation hours in summer was between 120 h and 160 h. The maximum value of effective precipitation hours was recorded in the piedmont windward area in the north of Beijing. The difference in effective precipitation hours between urban and suburban areas was not obvious, and the main impact of urbanization was on precipitation intensity. Secondly, summer precipitation in Beijing occurred mainly in the evening until midnight; from midnight to noon there was less precipitation. The average annual rainfall maximum appeared at 1700 LST reaching 3.2 mm/h. Furthermore, there was an obvious precipitation cycle, for which the main length of the period was about seven days. Thirdly, the differences in precipitation between urban and suburban areas were mainly caused by heavy rainfall, with urbanization leading to a reduction in weak precipitation events but a strong increase in precipitation events as a whole. Finally, the differences in continuous precipitation hours between urban and suburban areas was determined mainly by heavy rainfall; in most cases, the duration of precipitation was higher in the suburbs, occurring most commonly in the period from afternoon to midnight.